Recognition of two new species of freshwater crabs from the Seychelles based on molecular evidence (Potamoidea : Potamonautidae)

Abstract

Abstract. The Afrotropical freshwater crab genus Seychellum is endemic to the granitic Seychelles in the Indian Ocean (Mahé, Silhouette, Praslin, La Digue and Frégate). Here we describe two new cryptic species of Seychellum that represent two evolutionarily separate lineages of a previously monotypic genus. This raises to three the number of species of freshwater crabs known from Seychelles. Each species is endemic to either one island (Silhouette) or to a pair of islands (Mahé and Frégate, or Praslin and La Digue). The three species can be clearly distinguished as separate lineages by DNA analysis, haplotyping and examination of gonopod characters. The recognition of S. silhouette, sp. nov. (endemic to Silhouette) and S. mahefregate, sp. nov. (endemic to Mahé and Frégate) reduces the range of the type species, S. alluaudi (A. Milne-Edwards & Bouvier, 1893) to La Digue and Praslin. Both dispersal and vicariance may have played a role in shaping the present distribution patterns of the Seychellois freshwater crabs.

Phylogeographic structure and continued surveys of a Vulnerable South African freshwater crab (Potamonautidae, Potamonautes lividus): Implications for the IUCN Red Listing of the Afrotropical fauna

“…In a fine‐scale study of the burrowing freshwater crab Potamonautes calcaratus , restricted to ephemeral pans in the Kruger National Park, South Africa, Daniels et al (2002) reported moderate genetic structuring. In the Seychelles freshwater crab, Seychellum alluaudi , three distinct clades were observed that corresponded to different islands in the archipelago (Daniels, 2011) and were later described as three allospecies (Cumberlidge & Daniels, 2014). On Mahé Island alone, Seychellum mahefregate had an uncorrected sequence divergence value of 3.18%, and three distinct haplogroups were detected, coinciding with the central mountain ridges that are present on the island (Daniels, 2011).…”

“…In a fine-scale study of the burrowing freshwater crab Potamonautes calcaratus, restricted to ephemeral pans in the Kruger National Park, South Africa, Daniels et al (2002) reported moderate genetic structuring. In the Seychelles freshwater crab, Seychellum alluaudi, three distinct clades were observed that corresponded to different islands in the archipelago (Daniels, 2011) and were later described as three allospecies (Cumberlidge & Daniels, 2014 . Assuming that the species is now known from two isolated centres of distribution in KwaZulu-Natal and the Eastern Cape, the question arises as to whether dispersal among the two provinces, as suggested by the microsatellite data and, in one example, based on the COI data, is likely.…”

“…Nevertheless, decapod diversity and alpha taxonomy in the Afrotropical region remain relatively poorly documented, considering that large areas have not been surveyed for decades owing to civil war, conflict, and general inaccessibility. Despite these drawbacks, there has recently been a steady and concerted effort to document freshwater crab diversity in the Afrotropical region, resulting in the description of a new genus and several species new to science, many of which are narrow endemic species (Cumberlidge & Daniels, 2014; Cumberlidge et al, 2019; Daniels, 2017; Daniels et al, 2019; Mvogo Ndongo et al, 2019; Peer et al, 2017; Peer et al, 2015; Phiri & Daniels, 2013; Wood & Daniels, 2016). Within the Afrotropical region, 28% of the 94 freshwater crabs assessed by Cumberlidge et al (2009) fall into one of the three major threatened groups: 14 species are Vulnerable (VU), 10 are Endangered (EN), and two are Critically Endangered (CR).…”

Redescription of Potamonautes sidneyi (Rathbun, 1904) (Decapoda, Potamonautidae) and description of a new congeneric species from KwaZulu-Natal, South Africa

“…is not phylogenetically determined and may well reflect habitat similarities and environmental drivers, given their current distributions. This may support the lack of distinctive species-specific characters that appears to be a widespread trend for African potamonautids ( Daniels et al 2003 , Jesse et al 2010 , Cumberlidge and Daniels 2014 , Phiri and Daniels 2014 , Phiri and Daniels 2016 ).…”

A new species of trogloplacine crab of the genus Australocarcinus Davie, 1988 from a freshwater stream in Mahé, Seychelles (Crustacea, Brachyura, Chasmocarcinidae)

“…If all trogloplacines have abbreviated (or at least a semi-abbreviated) development and there are no free-swimming larvae, how did they disperse so widely? Despite hypotheses that primary freshwater crabs may have dispersed through Gondwanic connections (Ng et al 1995), the available evidence is that they are not old enough to have done so (see Daniels et al 2006; Cumberlidge et al 2008; Klaus et al 2009; Cumberlidge and Ng 2009; Daniels 2011; Cumberlidge and Daniels 2014); and as such, the disjunct distribution of A. insperatus sp. n. begs further studies.…”